change the style of the selecteditem in list box

I have a ScrollViewer :

<ScrollViewer Width="160" 
              VerticalScrollBarVisibility="Auto" 
              HorizontalScrollBarVisibility="Hidden" 
              Height="324" Canvas.Top="0" 
              BorderThickness="0" Padding="0">
   <ListBox x:Name="Snapshots" SelectionChanged="Snapshots_SelectionChanged" 
            Padding="0" Background="#FFF0F0F0" 
            BorderBrush="{x:Null}" VerticalAlignment="Top" 
            SelectionMode="Single">
      <ItemsControl.ItemTemplate>
         <DataTemplate>
            <Image Source="{Binding imageSource}" 
                   Margin="5" Stretch="UniformToFill" 
                   Width="120" Opacity="0.2"/>
         </DataTemplate>
      </ItemsControl.ItemTemplate>
      <ItemsControl.ItemsPanel>
         <ItemsPanelTemplate>
            <StackPanel Orientation="Vertical"  
                        VerticalAlignment="Top"  HorizontalAlignment="Center"/>
         </ItemsPanelTemplate>
      </ItemsControl.ItemsPanel>
   </ListBox>
</ScrollViewer>

How can I implement these features :

1. Change the opacity of the selected item (Image).
2. Change the default border style of the selected item (Image).

Thank you, it is working now. this is my style after updating :

<Style x:Key="ItemContainerStyle" TargetType="ListBoxItem">
        <Setter Property="Template">
            <Setter.Value>
               <ControlTemplate TargetType="ListBoxItem">
                    <Grid Background="{TemplateBinding Background}">

                        <vsm:VisualStateManager.VisualStateGroups>
                            <vsm:VisualStateGroup x:Name="SelectionStates">
                                <vsm:VisualState x:Name="Unselected" />

                                <vsm:VisualState x:Name="Selected">
                                    <Storyboard>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ImageBorder" Storyboard.TargetProperty="Visibility" Duration="0">
                                            <DiscreteObjectKeyFrame KeyTime="0">
                                                <DiscreteObjectKeyFrame.Value>
                                                    <Visibility>Visible</Visibility>
                                                </DiscreteObjectKeyFrame.Value>
                                            </DiscreteObjectKeyFrame>
                                        </ObjectAnimationUsingKeyFrames>
                                        <DoubleAnimation Storyboard.TargetName="contentPresenter" Storyboard.TargetProperty="Opacity" Duration="0" To="1"/>
                                    </Storyboard>

                                </vsm:VisualState>
                            </vsm:VisualStateGroup>
                        </vsm:VisualStateManager.VisualStateGroups>
                        <ContentPresenter
                              x:Name="contentPresenter"
                              Content="{TemplateBinding Content}"
                              ContentTemplate="{TemplateBinding ContentTemplate}"
                              HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                              Opacity="0.2"
                              Margin="{TemplateBinding Padding}" />
                        <Border BorderBrush="Black" BorderThickness="5" x:Name="ImageBorder" Visibility="Collapsed"/>
                    </Grid>

                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

and this is the listbox:

 <ScrollViewer Width="160" VerticalScrollBarVisibility="Auto" HorizontalScrollBarVisibility="Hidden" Height="324" Canvas.Top="0" BorderThickness="0" Padding="0">
                            <ListBox ItemContainerStyle="{StaticResource ItemContainerStyle}" x:Name="ListBox_AcceptedPhotos" SelectionChanged="Snapshots_SelectionChanged" Padding="0" Background="#FFF0F0F0" BorderBrush="{x:Null}" VerticalAlignment="Top" SelectionMode="Single">
                                <ItemsControl.ItemTemplate>
                                    <DataTemplate>
                                            <Image Source="{Binding imageSource}" Margin="5" Stretch="UniformToFill" Width="120" MouseLeftButtonUp="Image_MouseLeftButtonUp" />
                                    </DataTemplate>
                                </ItemsControl.ItemTemplate>
                                <ItemsControl.ItemsPanel>
                                    <ItemsPanelTemplate>
                                        <StackPanel Orientation="Vertical"  VerticalAlignment="Top"  HorizontalAlignment="Center"/>
                                    </ItemsPanelTemplate>
                                </ItemsControl.ItemsPanel>
                            </ListBox>
                        </ScrollViewer>